It is known to prepare a body constituted by a porous material by mixing powders or granulates of materials of the ceramic type, generally Al2O3, SiO2, TiO2, ZrO2, CSi, TiC, NSi and alkaline oxides such as Na2O, K2O, with a binder selected among organic materials such as acetic acid, sodium acetate, zinc acetate, propionic acid [1]. The process entails a reaction of the particles of metallic oxides with the binder, at a temperature below the sintering temperature at which the mixture is subjected to fire and drying.
A method is also known [2] for preparing a sintered porous body made of ceramic and/or metallic materials, which includes the mixing of an aqueous suspension containing powders of ceramic or metallic materials and of a binding resin (binder) which is a water-soluble polymer which can gel, and a blowing agent which activates the porosity of the gel, which becomes expanded; as the temperature increases, a porous metallic-ceramic material is formed by drying and sintering and its polymeric part is eliminated by pyrolization.
Another known method for preparing porous ceramic materials includes mixing ceramic powders with solid or hollow plastic pellets [4], [5] in a liquid in order to obtain a suspension, followed by drying and treatment in a high-temperature oven in an oxygen-free environment so that the plastic pellets that first act as adhesive for the ceramic powders are eliminated by pyrolysis, forming porosities.
It is also known that silica gels dissociate in the presence of water and alkaline metal hydroxides and can be destabilized further by other components, such as for example organic components known as electrolytes, which convert silica sol into gel by means of a phase transition depending on the degree of alkalinity of the aqueous suspension of silica, generating gel systems of a different kind [3]. A particular type of gel forms when the destabilization process of a colloidal solution of silica and alkaline compounds is activated by neutral reagents or acids, for example organic or mineral acids, esters and salts
Known processes for obtaining porous ceramic materials with high heat resistance generally entail a technology which is highly advanced from an engineering standpoint and very complicated and laborious to obtain refractory articles having a particular shape.
Moreover, in known processes, particularly advanced and sophisticated technologies which are not convenient in terms of production costs are applied to obtain large amounts of material in the industrial field.